Manufacture of transparent paper



June 14, 1932. 5 BOYER MANUFACTURE OF TRANSPARENT PAPER Filed May 27,1930 J I w W 1 7) a w A a I 1 I h, 7

Patented June 14, 1932 UNITED s'rA'rEs PATENT OFFICE SYLVESTER IBOYER,or roBTLANn, MAINE, ASSIGNOR To S. n. wAn'aEn COMPANY, or

BOSTON, MASSACHUSETTS, A CORPORATION or uASsAcHUSETTS MANUFACTURE OFTRANSPARENT PAPER Application filed May 27,

of glycerine, and then roll pressed and dried down to a proper residualcontent of water in a calender in which. hard steel rolls alternatedwith Soft rolls furnished with jackets of impregnated and compactedpaper or cloth. This arrangement of the calender rolls produced auniform compacting and smoothing effect which, however, in respect tocondensation of the paper web necessarily fell short of that which wouldbe effected by calendering between hard steel roll surfaces. On theother hand, the use of hard steel rolls alone I have found to beunsatisfactory for the reason that irregularities or departures fromtrue cylindricity of the rolls and irregularities in the thickness ofpaper web make the paper spotty, or non-uniform both in surface finishand degree of transparency. Thus portions only of paper calenderedbetween hard-steel rolls possess a higher degree of transparency thanthe entire area of slmilar paper after passage through a calender inwhich the hard and soft rolls alternate.

By means of the calendering apparatus herein to be described and of themethod of treatment performed thereby, one is enabled to Secure thehigher transparency in the paper product due to condensation of the1930. Serial N0. 56,023.

comprising 5 or 6, consists only of hard steel' rolls; the rolls Bintermediate between these top and bottom sets are soft rolls such asrepresented by metal rolls jacketed with im-- pregnated or induratedpaper or cloth. These soft rolls B constitute a set of at least two, andpreferably three, soft rolls.

The hard steel faced rolls are provided with means for internal heatingas usual, for the purpose of progressively drying the paper as it passesfrom the top to the bottom of the calender. A

My improved method of transparentizing paper is as follows. The paperweb indicated by P on the accompanying drawing, after having beeninitially dried, is moistened with water containing preferably not morethan 8% of glycerine, (for which a glycol, mannitol, or the like may besubstituted as an an equivalent) the moisture content of the I paperbeing brought to about 30% water on the dried paper weight. This paperenters the calender at the top, passing in succession between thehardsteel surfaces of the upper set, A, of hard rolls. This treatmentbetween hard unyielding surfaces condenses the body of the paper web,smooths it and enhances its transperency, but inevitably, for thereasons above indicated, the densely compacted areas do not extend overthe entire paper web, irregularly distributed portions of the paper webhave escaped the full effect of condensation and smoothing, and were thepaper to be withdrawn in this condition its physical irregularitieswould be too apparent. This defective condition is corrected by theoperation of the midway series of soft rolls B between which the paperweb passes after leaving the upper set of hard rolls. The deformabilityof the superficial portions of the soft rolls enables them to reach witheffective compression and smoothing action the hitherto untreated orpartially treated spots on the paper, and eifects thereon a condensationwhich approaches in degree to that of the hard roll condensed areas withsufliciently close approximattion as to produce in the paper web as awhole the appearance of substantial uniformity. The heat applied to theupper set of hard surface rolls should be so regulated with regard tothe rate of travel of the paper that when the web arrives at the set ofsoft rolls, it will have retained a moisture content sufiiciently largeto prevent injury to the web by the soft rolls which grip the web alittle more firmly than the hard rolls. This protective water contentshould be of the order of 10% to 12% on dried paper weight. This hasbeen found effective to guard against injury to the web by reason of theslight differential slip between the frictionally driven rolls. When thesoft roll treatment of the paper is completed, it is necessary to carrythe extraction of water by drying to that minimum percentage which isessential to preserve proper mechanical strength in the finished paperproduct. This final extraction of moisture must be accompanied bycontinued roll pressure, otherwise thepaper is liable to cockle and beinjured in quality by the formation of voids on the evaporation ofwater. I conduct the paper web therefore" from the set of soft rollsthrough the lower set C of hard rolls, which are so heated that when thepaper is delivered from the calender it will contain about 6% or 7% ofwater. This water content conserves the strength of the pa er, which isquite tough enough to be sa ely manipulated in folding and wrappingmachine. For the purpose of more nicely regulating the progressivedrying of the paper, fly rolls suchas indicated at D, D may be employed,over which the paper is led from and then back to the calender rolls.These fly rolls, provided with means for internal heating, may havetheir temperatures varied, and adjusted to fluctuating externalatmospheric conditions, and one or more of such fly rolls can beemployed, as occasion demands.

While it is technically possible to obtain the desired result by the useof water alone to moisten the paper before it passes into the calender,it is diflicult so to do because of variations in conditions both in andsurrounding the calender apparatus; the modicum of glycerine or itsequivalent in the moistening water serves to control evaporation so asto insure the proper content of moisture, both at the soft rolls and atdelivery of the paper from the calender.

Paper treated in the mode 'above described is uniform in superficialappearance, and possesses transparency to higher degree than paper ofthe same character as manufactured heretofore, this by reason of thesuperior condensation of the web over the major part of its area underthe action of hard roll pressure simultaneously on both sides of thesheet.

I claim:

1. Method of enhancing transparency of paper, characterized bysubjecting the paper while moist, to hard roll compression, meanwhilereducing the moisture content, then to soft roll compression while thepaper still contains enough moisture to prevent injury between softrolls, then subjecting the paper again to hard roll pressure whilereducing its moisture content to the percentage requisite to maintainpaper strength.

2. Method of enhancing transparency of paper, characterized bysubjecting the paper, with an initial moisture content of about 30% onthe dry paper weight, to hard roll compression, meanwhile reducing themoisture content, then to soft roll compression while the paper retainsa moisture content of the order of 12%, then subjecting the paper againto hard roll pressure while reducing its moisture content to a residueof the order of 6%.

3. Calender for transparentizing paper, comprising a series of pressurerolls, the first part and last part of the series consistingrespectively of a plurality of adjacent, contacting hard rolls, rollsforming an intermediate part of the series being soft rolls.

4. Calender for transparentizing paper, comprising a series of pressurerolls, the first part and last part of the series consistingrespectively of a plurality of adjacent, contacting hard rolls, rollsforming an intermediate part of the series being soft rolls, the hardrolls provided with internal heating means.

5. Calender for transpartentizing paper, comprising a series of pressurerolls, each frictionally driven by the next in series, the first partand last part of the series being hard rolls, rolls forming anintermediate part of the series consisting respectively of a pluralityof adjacent soft rolls, the hard rolls provided with internal heatingmeans.

6. Calender for transparentizing paper, comprising a series of pressurerolls, those of the first part and last part of the series being hardrolls, rolls forming an intermediate part of the series being softrolls, and fly-rolls provided with internal heating means.

7. Calender for transpareutizing paper, comprising a series of pressurerolls, each frictionally driven by the next in series those of the firstpart and last part of the series being hard rolls, rolls forming anintermediate part of the series being soft rolls, and flyrolls providedwith internal heating means.

I 8. Calender for transparentizing paper,

. comprisinga series of pressure rolls, those of this 23rd day of andfly-rolls provided with internal heating means. i

9. Calender for transparentizing paper, comprising a series of pressurer01ls,each frictionally driven by the next in series those of the firstpart and last part of the series being hard rolls, rolls forming anintermediate part of the series being soft rolls, the hard rollsprovided with internal heating means, and fiy-rolls provided withinternal heating means.

Signed by me at Cumberland Mills, Maine,

May, 1930.

SYLVESTER BOYER.

